Manufacture and use of PCBs, DDT and other persistent chlorinated hydrocarbons have ceased in the United States. However, large quantities of these toxic compounds remain dispersed in the environment where their distribution and fate are imperfectly characterized. Moreover, additional PCBs and other organochlorines continue to be added to the environment, particularly to natural waters where they contaminate the sediments and can be taken up by fish and then by humans. To investigate the sources and fate of organochlorine contaminants in the natural waters of the Hudson watershed, analyses of dated sediment core sections will be performed. Results from our initial funding period, have defined several areas of particular focus. A major source of chlordane to western NY/NJ harbor will be traced into the Hackensack and Passaic River watersheds. Chlordane is a significant contaminant of fish from this area and its residues have been found at elevated levels in local anglers (project 5). DDT-derived compounds will be measured in soils from urban parks. Our data from Central Park Lake sediments will be investigated using stable chlorine isotope rations. To our knowledge, this will be the first application of this powerful technique to the study of PCBs. This project will also involve interpretation of fish contaminant level data from the NYS Department of Environmental Conservation (DEC) that will produce a strong tie to a project , the urban anglers' study. Extracts of representative sediments will be supplied for use in biomedical projects 2 and 3. Our study of dioxin sources will link us closely to the EPA Superfund investigation of 80 Lister Avenue on the lower Passaic River. The closest collaboration will be with a project 6 which will provide the trace metal component of our multi-contaminant approach to persistent pollution in the Hudson watershed. As in the past, sediment sample collections will done jointly with scientists from project 6 and from the NYSDEC and all samples will be shared.